I have an odd issue that has cropped up on my wife's new CMMG 9mm Banshee build that was running great for about 450 rounds.  But now it's starting to have failure to eject problems.  I am suspecting that maybe this is an ejector spring issue but I've never had an issue like that before with an AR-15 so I was hoping maybe someone could tell just by seeing it in action in slowmo video before I go tearing it apart.  The shells are following the bolt straight back and bounce around inside the chamber before lazily falling out.  They dont seem to be getting thrown out forcefully.  I would expect that the shells would get tossed out about midway through the bolt traveling to the rear with some good amount of force that would toss it clear of the chamber before the bolt begins to move forward again.  I think it might be the ejector spring because I ran it with 5 different buffer weights, mag, no mag, and even tried a heavier buffer spring but nothing seemed to change the ejection weirdness.  It just doesnt seem to be ejecting cleanly.
[youtube]https://youtu.be/1b-ycn5mUkc[/youtube]

NOTE: For whatever reason,  the youtube video doesnt seem to embed properly here.  No idea why.  At least the link works I guess.

450 rounds is a bit early, but broken ejector springs have been a common occurance for RDB guns.

pretty common from what I've read and seen. Friends brand new rifle was having problems after 50 rounds. At @150 rounds a case blew out and kicked the mag out of the gun. We picked up more than a dozen cases that looked like belted mags. No thanks, the gun was returned to cmmg and so far they can't fix it. Friend just wants a refund.

https://c3junkie.com/?page_id=221

I removed the ejector spring (god I hate beating roll pins out,  whata pain in the ass).  The spring did not appear to be deformed but it's possible that it has been reduced in length/strength,  it was pretty spongey before I took it out,  not very stiff compared to my 5.56.  The 5.56 was VERY noticeably stiffer,  I cant depress it with my fingernail like I can with the 9mm RDB, so I can only assume that is a problem.  I dont have a fancy ft lb tester to find out what it's at so I'm just going to blindly replace the spring I guess.  Throwin shit at the wall until it sticks I guess you could say :/

IDK what I'm going to get for a spring yet.  Probably get a bunch of them to try different springs maybe.  Suggestions on springs would be appreciated from those who have had ejection issues on the 9mm RDB bolts and either solved them or keep a stack of springs on hand for replacement.  I dont do 3 gun matches or anything,  so replacing springs every so often is something we can do,  the wife just likes to shoot at nothing in particular but hates it when shit doesnt work lol.

Call CMMG support, they will send you a MK10 spring as a warranty replacement. They also sent me a new extractor, as they said that could be part of what's causing the problem. After replacing both parts I shot around 1,200 rounds so far without any issues.